Skin: vitiligo
Synonym(s): Snowflakes, Arabian fading syndrome, Pinky syndrome, Juvenile Arabian leukoderma
Introduction
- Cause: an acquired melanin pigmentary disorder.
- Signs: focal reduction of pigment in the skin (leukoderma) and/or the hair (leukotrichia).
- Diagnosis: history, clinical presentation, histopathology to rule out other causes.
- Treatment: observation only, topical steroids, tacrolimus?
- Prognosis: good.
Presenting signs
- Gradually expanding depigmented macules.
- Distribution of lesions can be symmetrical or segmental.
- No pre-existing lesions or pruritus present in affected areas.
- A subform of equine vitiligo: Arabian fading syndrome.
Acute presentation
- Not described, in humans 50% of affected people show lesions before age 20 years.
- Arabian fading syndrome: in young horses between 1-2 years of age, rarely in older horses.
Age predisposition
- 1-18 years.
Gender predisposition
- Females most commonly affected in some reports.
Breed/Species predisposition
- Arabians Arab.
- Quarterhorses Quarterhorse.
Pathogenesis
Etiology
- The exact cause of vitiligo is not known.
- Antimelanocyte antibodies have been found in animals including Arabian horses affected by the condition.
Predisposing factors
General
- Arabian fading syndrome: a genetic predisposition is suspected.
Pathophysiology
- To the authors knowledge the pathophysiology of vitiligo/leukoderma/leukotrichia in horses remains unknown.
- Three main hypotheses for pigment loss in human vitiligo have been advanced:
- Autotoxicity hypothesis: reactive melanin precursor molecules are thought to predispose melanocytes to destruction, possibly due to inhibition of thioredoxin reductase, a free-radical scavenger associated with the melanocyte cell membrane.
- Neural hypothesis: melanocytes originate from the neural crest and have characteristics of nerve cells; thus, neural injury has been advanced to explain dermatomal distribution of vitiligo.
- Auto-immune hypothesis (favored): melanocytes can be destroyed by humoral or cellular immune mechanisms; in humans and horses with vitiligo auto-antibodies against melanocytes have been found but it is unclear whether these antibodies are the cause or a result of the disease.
- A recent convergence theory adds to the above-mentioned mechanisms other factors such as genetic susceptibility, microbial dysbiosis, aberrant intercellular communication and oxidative cellular stress inducing novel autoantigens.
- Multiple mechanisms may contribute to development of vitiligo in individual horses.
Epidemiology
- The incidence of equine vitiligo has not been reported.
- One university clinic diagnosed vitiligo in 0.67% of their equine dermatological caseload.
- In humans approximately 2% of the population is affected and it is likely that the condition is also more common in horses as many clients may not seek veterinary attention for the problem.
Diagnosis
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Treatment
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Prevention
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Outcomes
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Further Reading
Publications
Refereed papers
- Recent references from PubMed and VetMedResource.
- Tham H L, Linder K E & Olivry T (2019) Autoimmune diseases affecting skin melanocytes in dogs, cats and horses: vitiligo and the uveodermatological syndrome: a comprehensive review. BMC Vet Res 15 (1), 251 PubMed.
- Montes L F, Wilborn W H et al (2008) Vitiligo in a Quarter horse filly: Clinicopathologic, ultrastructural and nutritional study. J Equine Vet Sci 28 (3), 171-175 SciDirect.
- Kanwar A J et al (2004) Topical tacrolimus for treatment of childhood vitiligo in Asians. Clin Exp Derm 29 (6), 589-592 PubMed.
- Montes L F et al (2003) Value of histopathology in vitiligo. Int J Derm 42 (1), 57-61 PubMed.
- Halder R M & Brooks H L (2001) Medical therapies for vitiligo. Derm Ther 14, 1-6 Wiley Online Library.
- Stannard A A (2000) Pigmentary disorders. Vet Derm 11, 205-210 Wiley Online Library.
- Le Poole I C et al (1993) Review of the etiopathomechanism of vitiligo: A convergence theory. Exp Derm 2 (4), 145-153 PubMed.
Other sources of information
- Scott D W & Miller W H (2011) Pigmentary Abnormalities. In: Equine Dermatology. 2nd edn. Saunders, USA. pp 389-397.
- Knottenbelt D C (2009) Pascoe’s Principles and Practice of Equine Dermatology. 2nd edn. Ed: Knottenbelt D C. Saunders, USA.
- Scott D W & Miller W H Jr (2003) Equine Dermatology. W B Saunders, USA.
- Yu A A (1997) Dermatologic Conditions Associated with Abnormal Pigment. In: Current Therapy in Equine Medicine. Eds: Robinson N E. W B Saunders, USA. pp 391-393.